1. Field of the Invention
The invention relates generally to electromagnetic clutches and, more particularly, to an improved dust shield for a compressor clutch assembly.
2. Description of the Prior Art
In a typical compressor clutch assembly, a rotor is continuously driven and the torque is selectively transmitted to the compressor crankshaft by a clutch mechanism. In such a compressor, the clutch assembly is normally located adjacent to the rotor on the side of the rotor opposite the compressor housing. Compressors are often operated in harsh environments, for example, in agricultural and construction machinery such as combines, tractors, or cranes. Compressors are also typically operated in other harsh environments. In these various applications, exposure of the clutch mechanism to dust and other destructive elements is likely to cause premature failure of the clutch components, particularly the clutch pulley bearings.
Some compressors are operated without a clutch pulley cover, thus allowing ambient air to flow uninhibited throughout the clutch assembly. Efforts to prevent this air flow, with its associated dirt and debris, have included attaching a pulley cover to a front surface of the pulley. Such a cover is typically screwed or bolted on, thus requiring a pulley diameter greater than that of the clutch armature to accommodate screw holes. This increases the size of the compressor assembly unnecessarily. Covers which screw or bolt on are also more difficult to assemble and, therefore, increase the cost of manufacturing the compressor clutch assembly.
Inventions in the prior art have been designed in an attempt to alleviate the above problems by providing a pulley cover which attaches to the clutch pulley without the use of screws or bolts. For example, U.S. Pat. No. 4,793,457 discloses a safety shield for a friction clutch mechanism. A resilient dust shield is secured to the rotor by a snap fitting.
Referring to FIG. 7, a prior art clutch assembly is depicted. A dust shield 50 attaches to the outer rim surface 34 of clutch pulley 24, thereby allowing the diameters of pulley 24 and clutch armature 44 to be substantially the same. Pursuant to the prior art, dust shield 50 attaches to pulley 24 and encloses front surface 30. Dust shield 50 is a cylindrical hollow part including an open end and having a diameter dependent upon the pulley to which the shield will be attached.
Referring further to FIG. 8, an annular land 68 on outer rim surface 34 is defined by annular groove 66 and front surface 30 of pulley 24. Annular land 68 cooperatively engages with annular recess 60 of dust shield 50. Annular stop surface 62 of dust shield 50 abuts a front surface 30 of pulley 24 to provide a seal between shield 50 and pulley 24.
This arrangement has several disadvantages. For example, when the clutch rotates with a high speed, dust shield 50 can easily become disconnected from outer rim surface 34 of clutch pulley 24. Also looseness in the assembly can be created because the centrifugal force associated with high speed rotation can cause the open end of shield 50 to expand radially outward. This looseness typically causes vibration and noise within the clutch assembly.